DEVIATIONS OF SOURCE BEARING IN THE EARTH–IONOSPHERE CAVITY WITH THE DAY–NIGHT NON-UNIFORMITY

Abstract

Subject and purpose. The Earth-ionosphere cavity resonator is characterized by the day–night non-uniformity. The impact of this non-uniformity on the field amplitude and its spectrum was addressed in literature, however, the modifications of the arrival angle of extremely low frequency radio waves caused by this inhomogeneity were not considered. In the present work, the source bearing deviations are obtained in the framework of the smooth day–night transition model. The source and the receiver are located on the zero meridian at points with coordinates 22.5° N and 22.5° S respectively, while the propagation path 5 thousand km long occupies two characteristic positions relative to the non-uniformity. One of them corresponds to 4 hr (the path lies in the night hemisphere) and the second one corresponds to 8 hr of Universal Time (the path is located nearby the morning terminator at the day side). Methods and methodology. The full wave solution is used to determine the propagation parameters of ELF radio waves. The field spectra are found using the 2D telegraph equations. Results. The following results were obtained: influence of the non-uniformity is absent when the center of the propagation path coincide with the center of the night or the day hemisphere, and it increases when the path approaches the day-night interface; the deviations of the source bearing may reach ~3°; frequency dependence of the source bearing has a shape similar to the Schumann resonance spectral pattern; a weak elliptical polarization is observed for a monochromatic signal, and its sign changes when the propagation path moves from one side of the day–night non-uniformity to another; temporal variations of the pulsed orthogonal components of the horizontal magnetic field and the Umov–Poynting vector have a complex shape, and this impedes determination of the arrival angle of a pulsed radio emission; the frequency response of a Schumann resonance receiver significantly changes the pulsed shape, however, the maximum deviations of source bearing do not increase in this case. Conclusions. Influence of day-night non-uniformity on the source bearing in the Schumann resonance frequency band does not exceed the level of natural fluctuations caused by the noise nature of the thunderstorm activity of the planet, and this significantly obscures the experimental detection of such deviations. Detection of the terminator effect is possible only for exceptionally powerful ELF transient signals.

Keywords

• day–night non-uniformity
• earth–ionosphere cavity
• schumann resonance
• source bearing